1. Field of the Invention
The present invention relates to a suck back valve which makes it possible, for example, to avoid liquid drip from a liquid supply port by sucking a predetermined amount of a fluid flowing through a fluid passage in accordance with a displacement action of a diaphragm.
2. Description of the Related Art
The suck back valve has been hitherto used, for example, in a production process for forming semiconductor wafers. The suck back valve has a function to prevent so-called liquid drip, i.e. a phenomenon in which a minute amount of coating liquid drips toward the semiconductor wafer from a supply port when the supply of coating liquid to the semiconductor wafer is stopped.
A suck back valve according to a conventional technique is shown by FIG. 5, further details of which may be seen, for example, in Japanese Utility Model Publication No. 8-10399.
The suck back valve 1 includes a main valve body 5 formed with a fluid passage 4 for making communication between a fluid-introducing port 2 and a fluid-discharging port 3, and a bonnet 6 coupled to an upper portion of the main valve body 5. A diaphragm 7, which comprises a thick walled section and a thin-walled section, is provided at a central portion of the fluid passage 4. The bonnet 6 is formed with a pressurized fluid supply port 8 which is connected to an unillustrated pressurized fluid supply source and to which a pressurized fluid is supplied in accordance with a changeover action of a directional control valve.
A piston 9 is fitted to the diaphragm 7, wherein a v-packing 10, which is slidable on an inner wall surface of the main valve body 5 and which functions as a seal, is installed on the piston 9. Further, a spring 11, which constantly presses the piston upwardly, is provided in the main valve body 5. Reference numeral 12 indicates a screw member which abuts against the piston 9 to adjust the displacement amount of the piston 9 so that the flow amount of the fluid sucked by the diaphragm 7 can be adjusted.
Operation of the suck back valve 1 shall now be explained in outline. In an ordinary state in which the fluid is supplied from the fluid-introducing port 2 to the fluid-discharging port 3, the piston 9 and diaphragm 7 are displaced downwardly in an integrated manner in accordance with action of the pressurized fluid supplied from the pressurized fluid supply port 8. The diaphragm 7, which is coupled to the piston 9, protrudes into the fluid passage 4 as shown in FIG. 5 by the two-dot chain lines.
When flow of the fluid through fluid passage 4 is halted, the piston 9 and diaphragm 7 are raised in unison under the action of the elastic force exerted by the spring 11, by stopping the supply of pressurized fluid from the pressurized fluid supply port 8. A predetermined amount of fluid remaining in the fluid passage 4 is sucked under action of a negative pressure produced by the diaphragm. Thus, dripping of liquid, which would otherwise be caused at an unillustrated fluid supply port, is prevented.
Incidentally, in the suck back valve according to the above-described conventional technique, for precise adjustment of the flow rate of pressurized fluid supplied to the pressurized fluid supply port, a fluid flow control device 14 is connected through a conduit 13, for example a tube. The flow control device 14 is formed separately from the suck back valve 1, and in addition to preventing pressure variations in the pressurized fluid supplied with respect to the pressurized fluid supply port of the suck back valve, also provides a function to control flow rate of the pressurized fluid supplied to the pressurized fluid supply port 8.
However, when using the suck back valve according to this conventional technique, an operation for interconnecting supply pipes between the suck back valve and the fluid control apparatus 14 becomes necessary, resulting in inconvenience. In addition, a dedicated space for installing the fluid pressure control apparatus 14 separately from the suck back valve 1 becomes necessary, resulting in the disadvantage that the installation space must be increased overall.
Further, as a consequence of the supply pipe (conduit 13) connected between the suck back valve 1 and the fluid pressure control device 14, flow passage resistance increases, with the disadvantage that the precision and responsiveness of the diaphragm is weakened.